Many mechanical devices use oil for lubrication purposes. In devices that use oil for lubrication purposes, it may be particularly important to periodically check the condition of the oil, such as, for example, the level and quality of the oil. Oil quality may change for a number of reasons, including as a result of oxidation, hydrolysis, thermal extremes, and the introduction of contaminants.
Marine powertrains are provided with what is commonly known as a lower unit or an outdrive, which extends below the water line. The lower unit or outdrive houses gears, which transfer power from the marine engine to a marine propulsion device, such as a propeller, provided on the lower unit or outdrive. The lower unit or outdrive also includes a gear casing that contains oil for lubrication of the gears.
It is a particular problem with marine powertrains that the oil in the lower unit or outdrive may become contaminated with water. Since the lower unit or outdrive sits below the water line during operation, the failure of a seal or the striking of an object may readily allow water to enter into the gear casing. Depending on the amount and duration of its presence, water within the gear casing may cause a number of undesirable consequences, including gear corrosion, increased gear and bearing wear due to a decrease in the effectiveness of the oil to act as a lubricant, complete gear failure, engine seizure, or a cracked lower unit or outdrive when the boat is removed from water and stored in cold weather climates. These consequences may translate into costly repairs or complete marine powertrain replacement.
One arrangement for checking the condition of oil involves using a conventional dip stick. While useful for checking the level and to a certain extent the quality of the oil, partially due to the fact that oil and water do not mix, it may not be possible to detect the presence of water by using a dip stick, particularly when the amount of water contamination is minimal.
Another arrangement for checking the condition of oil involves an oil reservoir located remotely from the gear casing and connected to the gear casing via conduits, such as hoses. The reservoir is typically placed in an easily accessible location such as near the marine engine of the marine powertrain and is typically made from a transparent material, such as plastic. Since the oil in the reservoir changes to a milky color in the presence of water, the presence of water may be visually detected from within the boat. Since in this arrangement the reservoir is positioned at an upper portion of the marine engine and the gear casing is located below the water line, gravity results in the gear casing becoming completely filled with oil. Completely filling the gear casing with oil increases the drag on the gears. This, in turn, decreases the efficiency of the power transfer from the marine engine to the marine propulsion device.
Yet another arrangement for monitoring the condition of oil involves the use of a variety of sensors, including, for example, capacitance sensors, optical sensors, or electrical resistance sensors. As just one example, since the dielectric constant of the oil is a function of the quality of the oil, those of ordinary skill in the art will appreciate that oil quality, including the presence of contaminants, such as water, may be determined by utilizing capacitance sensors to monitor the dielectric constant of the oil contained within the gear casing. Furthermore, those of ordinary skill in the art will appreciate that the capacitance sensor may be positioned so that in the event the oil level is below the position of the sensor, a dangerously low level of oil may be detected as well. Those of ordinary skill in the art will appreciate that capacitance sensors may monitor the dielectric constant in a number of ways, such as, for example, by outputting a voltage output, which varies according to the dielectric constant or by outputting an oscillating current frequency, which varies according to the dielectric constant. Regardless of the particular sensor employed, the sensor may be used in conjunction with a display or an alarm for indicating the oil condition or a problem with the oil condition.
Empirical analysis has demonstrated that in situations where the oil is contained in the gear casing along with a gas, such as air, i.e. in situations where the gear casing is not completely filled with oil, the oil and air may mix when the engine operates at high speeds to thereby create a foam-like mixture of oil that is aerated with gas. When this occurs, it may be difficult to reliably ascertain the condition of the oil using a variety of sensor technologies. As just one example, since the dielectric constant of the oil and gas mixture is different than the dielectric constant of liquid oil, making determinations of oil condition based on the dielectric constant of such a mixture may prove to be inaccurate. Empirical analysis has demonstrated that this oil and gas mixture phenomenon is acute according to the speed at which the marine engine is operated.
The present invention is directed toward an improved system, method, and computer program product for monitoring oil condition.